The plot was developed by the Pazzi family (with ‘pazzi’ perhaps fittingly translating to crazy/insane) together with other Medici rivals and enemies including Pope Sixtus IV and his bankers in Florence, the Salviati family and others. The Duke of Urbino is also believed to have agreed to provide troops to support the takeover bid.
As with most feuds, their beef with the Medici family was over land and power. Although the pope was very careful not to support murder, he was just as careful to imply beneficial papal treatment for anyone who were to aid in stripping the Medici of their powers in Florence and thus make way for his own advancements.
Thus, on Sunday, 26th April, 1478, an assassination attempt occurred inside the cathedral of Florence – Il Duomo – where brothers Lorenzo and Giuliano de’ Medici were attending mass. Giuliano was stabbed some 19 times, fatally wounding him, whilst Lorenzo was also injured but managed to escape. Further takeover action was abandoned when one of the Salviati and the archbishop became trapped inside a room.
The local population, at that time strong supporters of the Medici family, were enraged. Lorenzo de’ Medici, ruler of Florence at the time, asked the locals not to enact revenge. Nonetheless, many conspirators and their assumed accomplices were killed.
The luckier members of the Pazzi family were banished from Florence, stripped of all possessions, whilst others were imprisoned and tortured. Family members of the Pazzi family were tracked down throughout Europe. All references to the Pazzi name, including the coat of arms, were destroyed. Jacopo de’ Pazzi was even thrown from a window before being dragged through the streets naked and tossed into the Arno River. Salviati was strung up and hanged on the outer walls of the Palazzo Vecchio.
Lorenzo saved the several of the presumed conspirators, including the nephew of Pope Sixtus IV – a cardinal who was likely duped into his involvement.
Despite this, Pope Sextus IV was riled over the death of the archbishop and placed an interdict over Florence, with mass and communion not permitted. He then called upon the King of Naples to attack Florence. Lorenzo took the bold move of sailing direct for Naples, where he was held by the king for 3 months, until he was able to convince the monarch to take the side of peace.
The Pazzi Conspiracy had thus failed, and so spectacularly that the results were a greater support for the Medici and strengthened power for some decades to come.
The Pazzi family eventually got their own when in 1494, Piero de’ Medici was overthrown and many exiles, including the Pazzis, were allowed to return to Florence and take up positions of power.